Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/662

 T O U

T O U

TOTTA VILLA, in zoology, a name by which fome authors have called the alauda arborea, or common wood-lark. See the article Alauda.

TOUCAN {Cycl.) — Toucan, in zoology, the name of a very remarkable Brafilian bird, a kind of magpie, of a middle fize between our common magpie and the thrufh, but having a beak thicker and longer than its whole body ; this beak is hooked at the end, and is of a very thin fubffance, not exceeding the thicknefs of a membrane, and very light and hollow, yet bony in fubitance and very bright and mining. It has a fort of toothed edge, which prevents its fhutting clofely, and giving pafTage for the air, enables the bird to live without noftrils. It is yellowifh on the outfide and red within, and is covered with a fort of fcaly fubftance eafily fcraped off with a finger at the edge. Its head is large in proportion to its body, and is black on the crown, the reft of it and the neck and back are flightly variegated with white ; its bread is of a bright orange-colour, and its belly and thighs of a very fine and bright red, and the taii is black, but red at the end : it is on the whole a very Angularly beautiful bird. It is faid that it feeds on pepper, and Thevet affirms that it devours it greedily and returns it again undigefted, and that the natives gather up that pepper, and ufe it in their food, as lefs hot and acrid than the frefh pepper. See Tab. of Birds, N°. II. and Ray's Ornitholog. p. 88.

TOUCH-Halc, or Vent, in gunnery, is the fmall hole at the end of the cylinder of a gun or mufquet, by which the fire is conveyed to the powder in the chamber. In a firelock, cara- bine, or piftol, it is called the Touch-hole, but in a piece of cannon it is more properly called the vent.

TovcH-Needles, fmall mafles of gold, filver, and copper, each pure, and fimple, and in all the different combinations, pro- portions, and degrees of mixture, prepared for the trying gold and filver by the Toucb-ilom ; by comparifon with the mark they leave on it.

The metals ufually tried by the Touch-Hone, arc gold, fdver, and copper, either pure, or mixed with one another indifferent degrees, and proportions, by fufion. In order to find out the purity, or quantity of bafer metal in thefe various admix- tures, when they are to be examined, they are compared with thefe needles, which are mixed in a known proportion, and prepared for this ufe. The metals of thefe needles both pure and mixed, are all made into lamina: or plates, one twelfth of an inch broad, and of a fourth part of their breadth in thicknefs, and an inch and half long ; thefe being thus pre- pared, you are to engrave on each a mark indicating its purity, or the nature and quantity of the admixture in it. The manner of making the Touch-media is by the propor- tions of the mark, a weight of half a pound, or eight ounces, being divided into fixteen half ounces, the half ounces each into four drams, the dram into four penny- weight, and this into two half penny- weights.

Silver ToucH-Ncedla, thefe muft be only tempered with cop- per, and the proportion determined by the mark divided into half ounces and grains.

You muft ufe therefore for this purpofe one mark of fuch a weight that it may conftitute a fufficient mafs of metal for the making one needle, let it weigh for inftance one dram, then weigh fuch a mark of the pureft filver, wrap it up in a fmall paper and upon this write fixteen half ounces, which will fignify that the whole mark of this metal is the pureft filver, make the firft needle of this mafs.

Next weight fifteen half ounces of pure filver, and one half ounce of pure copper, wrap thefe both in a paper, and write on it fifteen half ounces, which will fignify that there are in that fmall mafs fifteen parts of pure filver, and one part of pure copper; make of this the fecond needle. In the fame man- ner go on with the reft, add two half ounces of copper to fourteen half ounces of filver, mark it fourteen half ounces make the third needle of this, and in the fame manner pro^ portion the fmall mafles of filver and copper for making the other needles, and put inferiptions upon every one in the fol-

lowing

Fortlie needle-

r '•— l5 l

2.— 15

3— '4

4— 13

5— 12 6.— 11 7— 10 8.- 9

9 — 10. — 11.— 12. —

'3—

14.—

IS—

L16—

g Half 01. of filver^

2

3

4 5

6 n g ^halfoz. of copper.

9

'3 14

U5J

When you have gone thus far, and have the metals in each of thefe proportions, wraped up in its fcparate paper ; put each feparately, into a new crucible never ufed for any operation, and adding a little borax melt them together in a very quick 4

fire, which muft be well kindled before with bellows : or what is yet better, throw them fuddenly into a hot crucible, and as foon as they melt, ftir them with a dry wooden peg, burnt at the end, and pour them immediately into an ingot. When this is done, wrap up each mafs, when cold, in its own paper again, and weight them fingly, in a nice ballancc. If they flill weigh a whole mark, they arc good ; but if there is any confulerable deficiency in their weight, it is a fign that your fire having been too weak, or of too long duration, has con- fumed as much copper as is wanting in the weight ; therefore this mafs muft be eiteemed ufelefs, and another made in its place in the fame proportion.

When this is all finifhed, make with a hammer out of each thefe fmall manes, a Needle, making them a little hot ; then engrave on each of thefe Needles, the number of half ounces it contains, as before marked on its paper ; that is, upon the firft 16, upon the fecond 15, and fo on, and then pierce them at one end, and running a filver wire thro' their eyes, collect them in order according to their different numbers. Thefe are the Silver Touch-Needles, made of the different al- lays of filver and copper.

In Holland they make ufe of the mint mark, divided into grains for the making their Needles. The firft Needle made of pure filver is faid to be of twelve penny-weights. The fecond is made of eleven penny-weights and eighteen grains, by the addition of fix grains of copper. The third is made of eleven penny-weights and twelve grains, by the addition cf twelve grains of copper ; and fo on, the proportion of filver decreafing always fix grains, that is, one quarter of a penny- weight at a time, and that of the copper being always wi- creafed in the fame proportion, till at laft the weight of the filver is reduced to one penny-weight, and that of the cop- per encreafed to eleven penny-weights, which proportion conftitutes the laft Needle.

It is needlefs however) to go through the whole feries of the Needles, by fo fmall progreffions to the very laft, for very delicate proportions cannot be very accurately diftinguifhed in the operation. ■Gold- Tovca- Needles. Thefe muft he mixt either with fileer alone, or with filver and copper, varioufly intermixed. This mixture is called allaying or carracting, and is determined with a mark divided into carraits, or weights of two fixth parts df an ounce. There is nothing to be obferved about the making of thefe Needles, befide what has been already faid in regard to the Silver Needles ; except that the proportions of the weights are determined in another manner. Thefe Needles are made according to the following divifion and order i and they all weigh one mark.

2. 3-

4- 5' 6.

7- 8.

9*

10.

11-

The firft is entirely of pure gold. 23 Car. 6 Gr.~) ("6 Gr.

23 Car.

22 Car. 6 Gr.

22 Car.

21 Car. 6 Gr.

21 Car

20 Car. 20 Car. 19 Car. 18 Car.

6Gr.

►pure gold*;

6G-. 1 Car.

1 Car. 6 Gr.

2 Car.

2 Car. 6 Gr.

3 Car.

3 Car. 6 Gr.

4 Car.

5 Car. J.6 Car.

> pure filver.

The decreafe goes on thus, by whole carra£ts, till the weight of the gold is arrived at one carract, and that of the filver at twenty three ; for after the ninth Needle you cannot make fo exact a diftindtion of the half carrafts. This mixture of gold and filver is called the white allay; but when copper together with filver enters into the mixture of the gold, then it is called a mixt allay. The Needles for trial of pieces thus debafed, are made of mixtures analo- gous to the former, except only that thofe portions which in the firft cafe were pure filver, here confift of copper and fil- ver mixt. Therefore you have here a double feries 5 for the mixture is either of two parts of filver, and one of copper, or of two parts of copper and one of filver. For inftance-,

The firft is of pure gold. 23 Car. 6 Gr."] f± Car.

6 Gr. "g J 1 Car.

>Z<

23 Car. 22 Car. 22 Car. 21 Car. 21 Car. 20 Car.

6 Gr. I B

> 3 < i Car. 4 Gr. > %J 8

6Gr

Gr. Gr. Gr. Gr. Gr. Car. Car. 2G1".

1 Car. 8 Gr.

2 Car. 2 Car. 4 Gr.

and fo on as in the foregoing.

If in this table you take pure copper inftead of pure filver, and filver inftead of copper, this gives you a third feries of golden Needles. And you may have a fourth by mixing with gold equal quantities of filver and copper in the fame proportion. Thefe allays of gold are much in ufe, but workmen may eafily employ a multitude of other variations, which compared with the already mentioned will be diftinguifhed in a thoufand diffe- rent ways by an experienced perfon, fo that it is neither pof- fible, nor neccflary to imitate them all. But that thefe golden Needles may not be too expenfive,

they